The present invention relates to polishing apparatus for polishing a semiconductor wafer or other articles, and in particular, to a carrier device adapted for use in such polishing apparatus and designed to controllably carry an object with the object held in engagement with the polishing surface of a turntable during a polishing process.
FIG. 5 shows a typical semiconductor wafer polishing apparatus wherein a polishing process, commonly known as "chemical-mechanical planarization" (CMP), is carried out to finely polish a semiconductor wafer. The polishing apparatus generally includes a turntable 200, a wafer carrier device 210 and a polishing surface dressing device 220.
The turntable 200 is provided on its upper surface with a polishing pad made of polyurethane foam, artificial leather or the like or a fixed abrasive plate and is connected to a drive shaft 201. The drive shaft is in turn connected to a motor (not shown) so that the turntable 200 is turned around its center axis. The wafer carrier device 210 includes a wafer carrier 211 in the shape of a disc and a motor 212 for ratating the wafer carrier 211 around its center axis through a transmission with a drive shaft 215 connected to the wafer carrier. The wafer carrier 211 is fluidly connected to a vacuum source (not shown) through a pipe 217. The pipe is connected to the drive shaft to positively hold a semiconductor wafer against the bottom surface of the wafer carrier 211 by vacuum. The polishing surface dressing device 220 includes a dressing tool 221 and a motor 222 for rotating the dressing tool 221 around its center axis. The wafer carrier device 210 and the dressing device 220 are mounted on pivot shafts 231 and 241, respectively, so that the wafer carrier 211 and the dressing tool 221 are brought into and out of engagement with the polishing pad of the turntable 200. Further, the wafer carrier 211 and the dressing tool 221 are both moved in a vertical direction by actuators or air cylinders 252 and 272.
During operation, the wafer carrier holds a semiconductor wafer on its bottom surface and brings it into engagement with the polishing pad on the rotating turntable 200 while being rotated around its center axis. After a desired numberof wafers are successively subjected to the polishing operation, the wafer carrier 211 is pivoted and brought out of engagement with the turntable and the dressing device 220 is pivoted to bring the dressing tool 221 into contact with the polishing pad on the turntable for conducting a dressing operation with respect to the polishing pad.
In such a polishing apparatus, there is a possibility that a crack may be created in a wafer which is being polished. If the polishing operation is continued in such a condition, the crack may become bigger so that the wafer carrier and/or the turntable may be eventually damaged. Further, a pressure controller may malfunction, whereby an inappropriate pressure such as an excessive pressure or insufficient pressure may be imposed on a wafer.